Particle separators are used to remove sand and dust from the air intake of gas turbine engines. A small fraction of the incoming air is often diverted to accomplish scavenging of the sand and dust from the separator. The pump that aids in the scavenging operation has to function in a very contaminated environment since there is a very high concentration of sand and dust in the separator exhaust air stream. Sand particles seriously pit and degrade the performance and life expectancy of a conventional bladed-fan type air pump when the gas turbine engine is used in a desert area.
My invention solves the fan blade erosion problem by means of an air pump provided with a self-bypassing path for the dirtiest fraction of the gas stream. The pump uses a dirt deflector installed upstream from the pump rotor blades. The deflector consists of a cone shaped inertial bypass which diverts the heavy sand and dust particles away from the pump's rotor blade which operates within a circular shroud located on the lee side of the deflector. Most of the sand and dust remains in the airstream passing between the periphery of the shroud and the outside wall of the apparatus. Air passing through the rotor blade stage recombines with the main stream of dirt laden air at an annular shaped ejector nozzle just downstream of the rotor blades. The high velocity turbulent air at the output of the ejector nozzle slows as it traverses the annular diffuser stage, at the same time undergoing an increase in pressure.
The self-bypassing feature of my invention greatly improves rotor durability for air pumps delivering large volumes of sand and dust laden air on a continuing basis.